(a) Field of the Invention
This invention relates to a process for restoration of ground water used in mining and more particularly, but not by way of limitation, to a process for removing uranium, selenium and other minerals from ground water for obtaining acceptable federal and state regulatory ground water levels. The ground water used in an in-situ leach uranium mining operation.
(b) Discussion of Prior Art
In other in-situ uranium mining operation, chemical reductants have been added to a mineralized geological formation to create reducing conditions within a mining zone. The reductants used for ground water restoration. Typically, the chemical reductants include sodium sulfide, sodium sulfite, and hydrogen sulfide. A major disadvantage to this method is that the chemicals have the potential, under certain conditions, for creating a dangerous atmosphere, which can be fatal to humans.
In U.S. Pat. Nos. 4,108,722 and 4,206,193 to Stover, a restoration process is described wherein an in-situ uranium mining operation injects bacteria into a mineralized sandstone formation. The bacteria has been previously cultivated in bioreactors on the above ground surface.
In U.S. Pat. No. 5,324,491 to Lovely, an enzymatic reduction and precipitation process of uranium is described using bacteria. This patent deals primarily with above ground bioreactors. The ground water is passed through the bioreactors and the uranium is precipitated out inside the bioreactor.
In U.S. Pat. No. 5,554,290 to Suthersan, a remediation method is disclosed using an in-situ anaerobic reactive zone to precipitate heavy metals from the ground water and to achieve de-nitrification. The in-situ reactive zone provides a permeable barrier formed by using indigenous bacteria when carbohydrates are injected into the ground. The carbohydrates are a nutrient source for the indigenous bacteria, which metabolize the food source for providing free electrons. Sulfates, nitrates and redox sensitive organics and metals act as the electron acceptors. The reduction of sulfate provides the sulfide in the ground water, which the metal contaminants react with to form insoluble metal sulfide compounds. The insoluble metal sulfide compounds precipitate out of the ground water as it passes through the reactive zone.
In U.S. Pat. No. 5,710,361 to Harrington et al., a process of adding nutrients inside a passageway created in waste stacks and earth materials is disclosed. The process promotes the growth of the indigenous bacteria therein for producing microbial sulfides. However, this patent doesn't disclose or mention the interaction of circulating ground water through a mineralized sandstone formation, especially in a deep underground sandstone formation with a confined sandstone formation. Additionally, this patent does not include treating uranium as a contaminant that can be remediated when the ground water is circulated through the sandstone formation.
In U.S. Pat. No. 5,833,855 to Saunders, a method of adding ferrous iron and a carbon nutrient source to ground water is described. This patent's biological reduction method relies on a co-precipitation of the metals with an iron sulfide compound produced by sulfate reducing bacteria. Also, this patent's injection solution may include sulfate-reducing bacteria.
The subject process for restoration of ground water differs from the above-mentioned prior art in that it relies on indigenous bacteria already present within a mineralized sandstone formation. The process produces insoluble compounds of oxides, sulfides and iron minerals in the ground water, which are dropped out of solution when circulated through the mined rock system.